Participants in both groups will receive G-CSF twice daily for 4 days. In the evening on Day 4, a dose of plerixafor will be administered. Apheresis will be initiated the next morning. Participants will continue to receive G-CSF twice daily and to receive the evening dose of plerixafor followed by apheresis the next morning for up to a total of 4 aphereses or until ≥5*10^6 CD34+ cells/kg are collected.